Abstract

This study originates from the increasing need for preserving groundwater resources as a major sustainable source of water supplied to all types of human consumers, particularly in semi-arid regions. In general, the number of water supply wells in a semi-arid region is large. Therefore, monitoring the quality of groundwater is usually carried out by successive steps of selecting a small number of sampled wells. The results of the groundwater monitoring and water quality analysis should provide input to decisions about possible measures leading to sustainability of the groundwater resources. The review of this study indicates that there are two general methodologies of selecting sampled wells: a) Random selection, and b) Systematic selection. We have tested the efficiency of various methods incorporated with these two methodologies. Our well sampling tests have been carried out with a hypothetic aquifer domain partly based on a small part of the Coastal Plain Aquifer (CPA) of Israel. This domain incorporates 4 monitoring wells and 63 water supply wells. Wells of the domain are sampled in 12 sampling steps. During the entire process of selecting wells and sampling we have followed the variation of important parameters of the groundwater quality, which are connected with the possible major objectives of the monitoring project. Regarding the random selection of sampled wells, our tests have indicated that random selection of sampled wells from a professionally divided domain can be more efficient than random selection of sampled wells from the entire domain as a single unit. Systematic selection of sampled wells can be most efficient, provided it is based on properly using the concept of well utility function and sampled wells are selected from a domain professionally divided into clusters of wells. Further, the optimal number of well clusters is identical with the number of wells selected in each step of well selection. And the definition of the well utility function should be connected with the major objectives of the groundwater quality monitoring project. Examples of such objectives considered in this study are: a) Identifying contours of contaminant concentration and possible sources of contaminants, (b) Identifying the contaminant concentration of the most productive wells, c) Identifying the flux of contaminants provided by the water supply wells into the water supply system, and d) Identifying wells with contaminant concentration higher than an adopted threshold concentration value.